This invention relates generally to internal combustion engines and, more particularly, to internal cumbustion engines for use in applications on board ships wherein the engine is used in a portable pump power system for damage control and firefighting purposes.
An engine of the indicated types must be capable of producing sufficient horsepower, must be light in weight, and must be capable of running on fuel of low volatility, such as diesel (DFM) or kerosene (JP5) type of fuel as opposed to gasoline which is highly flammable. Present-day diesel engines in a suitable horsepower range (of the order of 50 bhp) are much too large and heavy for portable applications. Further, present-day diesel engines do not have the ability to start unassisted at very low temperatures.
An internal combustion engine for use in portable applications of the indicated type would desirably meet the following criteria;
(1) The engine must be capable of starting without external power over a wide temperature range, i.e., from -21.degree. F. to +140.degree. F. PA1 (2) The engine must make about 48-50 horsepower at a speed not to exceed 6000 RPM. PA1 (3) The engine must be capable of running on either JP5 fuel or DFM fuel. PA1 (4) The above criteria must be met without the use of a battery or other external power source (other than manual) for starting of the engine.
It is the general object of this invention to provide an engine that meets the above-listed criteria and is suitable for use in a portable pump power system on board ship for damage control and firefighting purposes.
In accordance with the general object of the invention there is provided a novel and improved cylinder head, fuel system and ignition system for use on a commerical two-stroke internal combustion engine.
Briefly stated, the novel engine design in accordance with the invention utilizes the diesel technology of injecting the fuel directly into the combustion chamber combined with the flame front burning characteristics of a gasoline engine. The direct injection controls the fuel to allow high power (high cylinder pressure) operation without detonation by stratifying the fuel in the combustion chamber. Accordingly, the fuel/air mixture away from the fuel injector and spark plug is leaner and unable to detonate. The direct injection sprays two streams of fuel adjacent to the spark plug so that the misting effect from the injector allows ignition energy of the spark plug to ignite a very small amount of fuel in the combustion chamber. This flame front spreads across the combustion chamber becoming more effective in burning the fuel as the engine heats up. The direct injection avoids detonation at higher powers (higher combustion pressures) by controlling the dispersal of fuel in the combustion chamber.
The relationship between the spark plug and the fuel injector spray pattern is most critical for cold starting and power. The fuel injection spray plumes must be close enough to the spark plug so that a fine mist of fuel is available at the spark plug for ignition purposes. At the same time, the fuel injection spray plumes must not be too close so that the fuel is too close or impinges directly on the spark plug so that it will become wetted and will not fire properly. Accordingly, the plume angle and the distance from the spark plug (as well as the plume shape) are important to the proper starting characteristics.
In accordance with the general object of the invention, the combustion chamber design is such that it achieves the proper performance desired. To this end, an open combustion chamber design allows spent exhaust gases to be scavenged efficiently for better power at high engine speeds. Thus, the combustion chamber consists of a simple bowl with the injector and the spark plug located within the bowl.
In order that the engine both start reliably and produce high power, there is provided a variable fuel injection timing system. For starting purposes, the fuel injection and the spark are timed so that both occur at a time close to one another and close to the piston top dead center (TDC) position. However, as the throttle is increased, the ignition timing is increased to 20.degree. before top dead center (BTDC) while the injection timing is increased at a greater rate up to 150.degree.-180.degree. before top dead center (BTDC).
In accordance with another feature, the engine oil is injected at the intake manifold so that the crankcase of the engine is occupied by an oil/air mixture. It is important that no fuel is in the crankcase because JP5, unlike gasoline, does not readily evaporate from the oil whereby the JP5 dilutes the engine oil and therefore reduces engine life. This problem is avoided by injecting all the fuel into the cylinder head as described above.
It is noted that the various engine modifications and improvements as described above are all restricted to the cylinder head, the fuel system and the ignition system. Thus, these improvements can be applied to a stock cylinder block wherefore it is possible to refit the system of the invention to almost any gasoline two cycle engine. Accordingly, the engine in accordance with the invention can utilize a production cylinder block with its years of field and production experience as opposed to constructing a completely new engine. Further, the engine of the invention has enhanced reliability and can be produced at an acceptable cost.
It is noted that an engine in accordance with the invention can be constructed of a piston-type internal combustion engine weighing less than 100 pounds and producing up to 50 bhp.